Most concrete finishing procedures are really multi-step ones involving the use of several different tools and techniques to first work or consolidate the concrete and then smooth its surface. The main purposes of the working step are to remove air voids and excess water and to bring a thin layer of cement and fine aggregate to the surface which can then be finished by hand or machine as desired. Ideally, the working step will accomplish its purposes without unduly submerging the coarser aggregate and thereby destroying the general uniformity of the concrete mix.
In a common technique, concrete is worked with devices generally referred to as jitterbugs or roller packers after which a float is passed over it to give the concrete a relatively smooth surface which can be left as is or further finished. In most current techniques, the two steps of jitterbugging and floating are done separately using different tools; however, several patented floats have been equipped with vibrators in an attempt to perform these two steps with a single tool. Examples of such patented devices are U.S. Pat. Nos. 3,515,042, 3,515,043 and 3,547,014 to Austin, 2,282,248 to Davis, 2,514,626 to Clipson, and 3,376,798 to Bodine, and French Pat. No. 726,300 to Rand.
Of these patented devices, the three tools of Austin all have the distinct disadvantage that the drive for the vibrators is mounted on the float itself adding undesirable weight to it and making it impractical for use with higher slump (i.e., water) concrete mixes. Mounting the vibrator drive on the handle for the float as in U.S. Pat. No. 2,289,248 to Davis relieves some of the weight problems of Austin; however, it is believed to be preferable to have a remote power source as in the case of Clipson, Bodine, and Rand wherein the vibrators on the float are pneumatically or electrically driven and the weight of the power source is not carried by the tool at all. As between the vibrators of Davis and Bodine and those of Clipson and Rand, the rotating ones of Davis and Bodine versus the piston-type ones of the other two patents are believed to be preferable as far as their ability to bring a thin layer of cement and fine aggregate to the surface and remove air voids and excess water from the concrete mix. However, even these tools as well as all the other prior ones have limited ranges of frequency and amplitude and cannot be easily adapted for different slump (i.e., wetness) conditions of the concrete mix.
For the most part, any changes in frequency and/or amplitude in all of these prior art tools are limited to varying the output of the power source (e.g., increasing the motor speed or air pressure). For small variations in slump, such changes may well suffice. However, large variations in slump conditions (e.g., one-half inch to seven inches) require a widely varying range of frequencies and amplitudes for the proper working. Consequently, if a tool's frequency and amplitude cannot be readily changed over a wide range, the finisher must then keep several different tools on hand in order to be able to work the various slump conditions as the wrong frequency and/or amplitude can result in overworking the concrete and driving the coarse aggregate too far down in the slab thereby destroying its uniformity or underworking it and leaving undesirable air voids and water in the mix. Obviously, if a finisher has a tool with limited frequency and amplitude ranges and encounters an unexpected slump condition not within the tool's range, the concrete may well set up before the finisher can find a suitable tool or modify his present one accordingly. For example, the amplitude of Davis could be increased by replacing the eccentrically weighted bar with a larger one. However, this would only serve to create more undesirable weight on the float and an operator might well find that by the time he replaced the larger bar in the bearings of Davis and checked the dynamic balance, the concrete may well have already set up. Also, numerous jobs such as overlaying old concrete on bridge decks and laying patios, driveways, and sidewalks seeded with expensive surface rock often present unexpected concrete conditions requiring a relatively precise frequency and/or amplitude to properly work the concrete and set the surface rock in it. In such situations, the frequency and/or amplitude characteristics of a tool may be inappropriate and if its limited range of adjustments falls out of the ones needed, the tool is essentially useless.
It was with the above observations in mind that the concrete finishing tool of the present invention was developed. With the tool of the present invention, the advantages of a remote power system as in Rand and Bodine are combined with an improved vibrator design to produce a vibrating float whose frequency and amplitude can be easily and quickly adjusted over a wide range to handle varying slump conditions on the order of one-half to seven inches.